Correlation between the circadian sleep propensity rhythm and hormonal rhythms under ultra-short sleep-wake cycle

The aim of this study was to clarify effects of hormonal and temperature rh ythms on circadian fluctuations of sleep propensity. Ten healthy females un derwent 24-h sleep deprivation and entered the circadian sleep propensity a ssessment setting under the ultra-short sleep-wake schedule. During the exp eriment, sleep propensity rhythm, rectal temperature, and 24-h serum hormon e profiles (melatonin, cortisol and thyroid-stimulating hormone) were inves tigated. The circadian sleep propensity rhythms had two apparent peaks (aft ernoon and nocturnal peaks) and a trough (nocturnal sleep gate). The timing s of the nocturnal sleep gate and the nocturnal peak were correlated exclus ively with temperature and melatonin rhythms (P < 0.05), while that of the afternoon peak was significantly correlated with habitual wake time and mel atonin rhythm. These results indicate that the circadian sleep propensity r hythm is influenced not only by the circadian pacemaker, but also by sleep habit.